The present invention relates to a plastic sealed semiconductor device.
A plastic sealed semiconductor device having a semiconductor chip sealed with resin is subjected to thermal stress due to the difference in thermal expansion coefficient between the sealing resin and the semiconductor chip to be sealed thereby. With such thermal stress, an insulating film covering a major surface of the semiconductor chip tends to be cracked or an uppermost wiring layer of the chip tends to slide. The closer the portion of the semiconductor chip to a corner thereof provides the higher the chance of occurrence of such phenomena as sliding of the wiring layer.
There have been various approaches for preventing such defect as sliding. An example thereof is disclosed in JP-A-2-297953 in which a dummy conductive film is provided outside of the uppermost wiring layer. Such dummy conductive layer may be formed simultaneously with formation of the uppermost wiring layer. The function of such dummy conductive layer is to absorb compressive stress of sealing resin which is a main source of the sliding, etc., to thereby protect the wiring layer against sliding. This approach is considered practical since it is independent from choice of material for reduction of the difference in thermal expansion coefficient and does not require any additional fabrication step. However, there may be a risk of sliding of the dummy conductive film itself.
In the technical field of semiconductor integrated circuits, there is the continuous trend of increasing circuit integration density and miniaturizing circuit elements. For example, for a semiconductor memory, the number of bits to be stored has been increasing at a rate of four times per several years, while an area to be occupied by the memory chip is restricted up to about twice owing to the miniaturization effect of the constitutional components. With the increased size of the semiconductor chip, the phenomena such as above-mentioned slide, etc., tends to occur more easily. Further, due to an increase of use of the semiconductor device under severe environment such as on a vehicle or in desert area where thermal stress to be exerted on the semiconductor chip is considerable, the reliability of the semiconductor chip is highly required.